During a speech at NATO headquarters today, German chancellor Angela Merkel said, “It is not isolation and the building of walls that make us successful, but open societies.”

Oh, and did we mention Donald Trump was there? Like, right there? She called him out to his face moments before he addressed the assembled world leaders.

In case you have somehow forgotten, one of Trump’s biggest campaign promises was that he would build a wall of some sort along the southern border of the United States. Since he became president, he’s learned that the details are a little more complicated than the enduring chant of “who’s gonna pay for it? Mexico!” made them seem, but he hasn’t backed down on the promise anyway.

Merkel spoke in front of a fragment of the Berlin Wall, which she said “embodies the history that — during the Cold War — has left its mark on NATO for many decades.”

She spoke of the importance of tearing down walls and working together.